This invention relates to an oxygen concentration detecting apparatus, and more particularly to an oxygen concentration using an oxygen ion conduction type solid electrolyte.
Conventionally, there has been a prior art apparatus for controlling an electromotive force, generated in a sensing cell, at a specified value, and detecting an oxygen concentration from a value of current flowing in a pumping cell. There has been another prior art apparatus for limiting the above-mentioned current value to 80% of the limiting current to ensure a longer durability of the sensor in the above-mentioned detection (SAE880133, for example).
However, when an apparatus mentioned above for detecting an oxygen concentration from a current value of 80% of the limiting current is used in an intake pipe, since the oxygen concentration of the suction pipe is higher than that of the exhaust pipe, the pumping current shifts in a large measure to a higher side of oxygen concentration by a pressure pulsation in the intake pipe. This makes it impossible to detect the oxygen concentration with high accuracy, so that emission increases and the emission cannot be limited within the regulated value.